Tower cranes

ABSTRACT

A slewable tower crane comprises upper and lower hinged mast elements, the lower of which carries a carriage reciprocated by a screw jack. The carriage is connected by rods to a fixed portion of the slewable superstructure of the crane, and by a toggle system to the upper and lower mast elements, so that operation of the screw jack raises and lowers the mast elements with a folding action. The upper end of the upper mast element hingedly carries a horizontal jib comprised of two telescoping sections.

United States Patent 9 [72] Inventor Pierre Joseph Pingon 5, Avenue du Parmelan, Annecy (l-laute Savole), France Appl. No. 846,792

3,433,368 3/1969 Durand........................

[ l [22] Filed Aug. 1, 1969 [45] Patented Aug. 3, 1971 FOREIGN PATENTS 8/1966 GreatBritain................

Primary Examiner-Harvey C. Homsby Attorney-Young and Thompson [32] Priority Aug.30, I968,Dcc.24, 1968 [33] France [31] 164,641 and 180,317

ABSTRACT: A slewable tower crane corn rises up er and P P l 54] TOWER CRANES lower hinged mast elements, the lower of which carries a carl6 Cl i u Dnwin t riage reciprocated by a screw jack. The carriage is connected by rods to a fixed portion of the slewable superstructure of the [52] 11.8.

crane, and by a toggle system to the upper and lower mast elements, so that operation of the screw jack raises and lowers 1366c 23/62 the mast elements with a folding action. The upper end of the 212/46, 46 upper mast element hingedly carries a horizontal jib comprised of two telescoping sections.

PATENTEDAUB 315m 3 596 772 SHEET 1 0F 5 p/ERRE JOSEPH/00160 BY r-JW IFLESHfI-RYTE? PATENTED AUG 3197! SHEET 5 [IF 5 5y rJM HTr-Y TOWER CRANES v The present invention relates generally to tower cranes and has more particular though nonexclusive reference. to tower craneshaving a horizontal jib.

Cranes of this type are very good and satisfactorylifting and distributing devices .on working sites but they present several disadvantages among which the following ones may be cited, namely:

a. Their erection is a lengthy and expensive job which requires specially skilled operators.

b. They are liable to be too easily blown and tumbled down when heavy or gusty winds prevail.

c. After being erected, they cannot be shifted along except on tracks the installation of which is an expensive operation.

The object of theinvention is to remedy these disadvantages of existing tower cranes and to permit the provision of an im-' proved tower crane, particularlyone havinga horizontal jib the erection and dismantling of which can be effected almost instantaneously without anydirect human manipulation by a mere remote control as an ordinary operating motion (lifting,

rotation or the like).

There are thus remedied not only.the aforesaid disadvantages in connection with. the erection and'the dismantling of the crane but also those resultingfrom .wind action and relating to the displacements of the crane inasmuch as this improved crane can be easily folded down when heavy wind blows so as to stave off anyaccident and, moreover, it is only sufficient for shifting the crane along to fold it down and to erect it again on the new working site so that a translational movement of the crane becomes an easy and dangerless operation. I 7

According to the invention an improved tower crane is provided having a horizontal jib and comprising a carrier chassis or frame equipped with several carrier trains, a revoluble orientatable superstructure fitted upon said chassis througha slewing or swiveling device and a mast made up of two hingedlyinterconnected elements and mounted upon said superstructure and characterized by the fact that the lower element of the mast is hinged at one .end to the superstructure while the upper element is itself hinged at the other end of said lower element so that these two elements may be swung between a horizontal inoperative positionin which they are 7 preferably superimposed and a vertical operation position, a

carriage of the like being guided on said lower element of the mast, a mechanism controlling the motion of said carriage upon said mast element, at least a rod connecting said carriage with a stationary pivot of the superstructure remote from the hinge of the lower mast element on said superstructure, whereby said lower mast element is angularly shifted between its horizontal inoperative position and its vertical operative position or vice versa when said mechanism is operated, and a set of links connecting said carriage or another point of the toggle system made up of the superstructure and the lower mast element with its upper element so as automatically to lift said upper element responsive to the lifting motion of the lower element and conversely its automatic folding motion together with the lower element.

According to an apparently advantageous constructional placement'of the upper element'with respect to said lower element thereby ensuring automatic lifting or folding down motion therewith.

I According to a useful feature, the lower element of the mast is hinged adjacent one end of the superstructure, which carries near its otherend the crane counterweight, and assumes when in inoperative position a horizontal position forming an extension of said superstructure, and the upper element of the mast may have a length larger-than that of the lower element so as to extend 'when in inoperative position over the latter and at vantageously constituted by at least two telescopically interengaged lengths which, when in inoperative position, occupy a fully home tucked in position so as reduce the overall length during transportation and lifting action, the first length being hinged to the mast top and connected through tie bars fonn, the superstructure carries a pedestal and the aforesaid carriage and one or several hinged points provided thereon are connected with said pedestal.

The mechanism for controlling the motion of the carriage advantageously comprises a lead screw cooperating with said carriage which is so arranged that a portion of the carriage;

and guys with the lower frame so as to hold up the jib. The other length of the jib which is advantageously of triangular cross-sectional shape is shiftable over rollers in and on the first jib length, control means being provided for operating the telescoping motion'of the second jib length relative to the'first jib length. Advantageously such control means comprise a cablereciprocatory device extending between an actuating device such as a winch fitted for example on the mast and a jockey pulley fitted upon the first jib-length, one runof the cable being connected with the second jib length for performing the telescoping action.

The sheave control of the'lifting cable for the crane is advantageously performed by engaging said cable over a pair of jockey pulley one of which is provided at one end of the jib while the other one is carried by the second jib length adjacent its portion supported by the first jib length so that the cable length or the position of the lifting hook heightwise should be independent of the telescoping position of the first jib length with respect to the first one.

Still according to a further feature, the second jib length carries a lifting carriage or trolley of conventional structure connected at one point of an endless cable extending substantially over the entire span of the second jib length and secured adjacent the free end of the first length so that the telescoping motion of the second jib length also causes a motion of the trolley, these two motions being controlled from one and the same mechanism.

Yet according to a further feature of the invention, the crane jib remains hinged to the upper element of the mast when in inoperative position, said jib being connected with the crane superstructure by a rear tie bar made up of two pivotally connecting parts, the pivotal point between said parts being connected with the hinge between the two mast elements so that the raising motion of the mast also causes a raising motion of the two parts of the aforesaid rear tie bar and consequently a raising motion of the crane jib up to its horizontal operative position.

Yet according to another constructional feature, the second sliding jib length has a smaller cross-sectional area than that of plemented by other rollers distributed lengthwise of the first jib length.

Still under theinvention, the lower face of the first jib length has a pair of members providing a track on which the rollers of the crane trolley may roll and the second sliding length carries adjacent its free end, which remains outside the first jib length in the fully telescoped condition of both jib lengths, elements providing a rolling track which, when the second jib length occupies its fully retracted position, build an extension of the rolling track for the first jib length.

Still under the invention, the lifting cable is trained over a pulley provided at the top end of themast, over the trolley pulleys, over a jockey pulley arranged at the free end of the second jib length and over a further pulley provided at the foot end of said second jib length before being secured at a position on the first jib length. This arrangement has for its advantage that it does not alter the height of the lifting hook during the telescoping motion of the second jib length with respect to its first length.

Also under the invention, the trolley control cable extending from the directing winch is trained over a pulley provided at the foot end of the jib and is fastened to the trolley and then over another pulley provided at the top end of the second jib length, then back inwardly of the latter and afterwards over a pulley provided at the foot end of said second jib length and finally backwards over a further jockey pulley carried by the first jib length and attached to the directing winch.

In accordance with still another feature of the invention, there are provided a locking device adapted to hold the second jib length in a fully retracted position with respect to the first jib length as long as the trolley is upon the latter, also means ensuring an unlocking action of said device when the trolley reaches the end of the second jib length. Another locking device holds the trolley upon the second jib length as long as the latter is partly disengaged from the first jib length, and means control the unlocking action of said other device when the second jib length reaches a fully retracted position with respect to the first jib length. Such an arrangement permits the trolley and the telescoping action to be controlled from a single winch or the like. The transfer of said trolley from one jib length to the other is only possible in the fulltelescoping position i.e. merely when the rolling track for the second jib length is abutted against therolling track for the first jib length, thereby providing a particularly safe assembly.

In order that the invention may be more easily understood and carried into practice, it will be more fully described hereafter with reference to the accompanying nonlimitative drawings wherein:

FIG. 1 is a diagrammatic elevational view of an embodiment of the crane mast according to the invention.

FIG. 2 is a diagrammatic elevational view showing the method of controlling the raising motion of the crane jib when the crane is being erected.

FIG. 3 is an edge view of a crane jib having a telescopic structure.

FIG. 4 is a cross-sectional view along the line IV-IV of FIG. 3.

FIG. 5 is a view similar to FIG. 3 showing how the lifting cable is guided by pulleys.

weight 7 arranged adjacent the rear end of the superstructure. The latter is provided near its front end with an axis 8 about which is arranged for pivotal motion the lower element 9 of a mast made up of two elements 9 and 10 hinged together by an axis 11 fitted upon the rear face of the mast. It will be seen that in the present construction, the lower element 9 of the mast is shorter than its longer element 10, the difference between their respective lengths being substantiallyequal to the longitudinal extent of the superstructure 5. Owing to this con- FIG. 6 is a view similar to FIGS. 3 and 5 showing the control powered axles 2 provided with wheels 3 or tracks, said frame preferably includingfoldable arms diagrammatically shown at 4, associated with jacks which, during the operation of the crane, impart to the entire machine the required stability.

The chassis or frame 1 is surmounted by a revoluble or swiveling superstructure 5 which rests upon said frame through the medium of a slewing annulus with balls 6. The superstructure 5 carries the powered unit (not shown) for reducing the slewing motion, a winch (not shown) and a counterstruction, when in inoperative position, the lower element 9 of the mast may extend horizontally while forming a continuationof the superstructure 3 while the upper element when folded down upon the lower element also extends over the superstructure.

The superstructure 5 comprises a pedestal 12. The lower element 9 of the mast is provided on its front face (which is downwardly directed when in inoperative position) with a guide 13 through which a carriage 14 is movable, said carriage forming as it were a nut member cooperating with a suitably joumaled' lead screw 15 capable of being rotated from a power-reducing unit 16 also supported by the lower element of the crane mast and energized in conventional manner.

The carriage 14 carries trunnions 17 connected by rods 18 with hinge points 19 provided on the pedestal 12 supported by the superstructure 5 on either side of the mast. Each trunnion 17 carries a rod 20 connected with a hinge point 21 from which a pair of links extend, said links being respectively connected with stationary hinge points 24, 25 provided on the mast elements 9, 10, adjacent the front faces of said elements.

It will be noticed from an examination of the drawings that the hinges 19 are situated slightly to the rear of the upraised mast and as high as possible due regard being paid to the overall volume.

Assuming the motion to be started from the folded position shown in solid lines in FIG. 1, the raising of the mast takes place as follows: The power unit 16 is controlled for moving the carriage 14 on the lead screw 15 along the mast element 9 away from said unit 16. As the points 19 are situated over and rearwardly of the hinge 8, there is produced a raising motion of the lower mast element 9 since the connecting rods 18 are of invariable length. Moreover, when the points 17, 24 are brought nearer together, there is a tendency for the angle -defined by the rigid rods 20, 22 to be reduced, its apex 21 being pushed away from said element 9 and through the medium of the rigid rods 23 for the upper mast element 10 to be automatically raised as its lower element 9 is raised. Consequently the mast unfolds itself. The lengths of the connecting rods and the positions of the hinges are obviously such that when the lower mast element 9 reaches its vertical position, the upper mast element 10 forms an extension of said element It will be understood that at the end of the stroke, when thrmast is vertical (position 9 and 10') the mast is positively held by the connecting rods 18 which then occupy the 18' position and by the toggle system 20-22-23 which is then in the 20'- 22-23 position. The complete mast is then in operative position and is positively held in this position without any locking action. The raising motion has been achieved by a mere depression of a button which controls the electric energization of the power unit 16. The folding down motion of the mast may be performed by a similar action subject to the power unit 16 being actuated in the reverse direction.

As previously indicated, the upper mast element may be combined with telescoping means of any suitable type thus permitting the mast height to be increased after it has been raised.

A description will now be given with reference to FIG. 2 of the way the crane jib is connected with the aforesaid toggle system so as to, perform its automatic lift as the mast is'being' raised.

As stated hereafter, the crane jib is made up of two or several lengths or sections. However only section 27 hinged at 28 to the upper mast element 10 is shown in FIG. 2. Such jib length 27 is associated with guys 29 and a set of beams 30 connected with said length at 31.

Point 32 of this set of beams 30 is connected by a pair of tie bars 33, 34 hinged at 35 with point 36 of the crane superstructure 5. Hinge 35 between the tie bars is connected by a rod 37 to the hinge 11 between the mast elements.

The lengths and the hinge points of the tiebars 33, 34 and rod 37 are such that in inoperative condition the sum of the lengths of the tie bar 34 and rod 37 is equal to the distance between points 36 and 11.

It will be easily understood from an inspection of FIG. 2 that as the mast is being raised as above stated, the tie bars 33, 34 exert from a given position, a tractional stress upon the set of beams 30, thereby moving the crane jib off the upper mast element and progressively moving the same upwards as the mast is being raised, to a horizontal limit position when the mast has reached verticality. Both tie bars 33, 34 then form mutual extensions of each other. However, in order to avoid any action of said tie bars upon the mast when in operative position, the rod 37 is preferably made up of two mutually hinged elements, for example by a pivot 38 and having a total length larger than the distance between points 35 and 1 1.

It will be seen from the foregoing that the overall size as erection is being performed is equal to the one obtained during transportation and, moreover, that the stability of the entire assembly during the raising action is adequately ensured by the normal counterweight 7 of the crane.

In 7 the showing of FIG. 2, the crane elements are represented in partly raised position and are designated by the same reference numerals as in the folded down position but provided with a dash.

In the constructional form as shown and as visible in F IGS. 3 to 6, the crane jib is made up of two telescopically interengaged lengths or sections 27, 40. Owing to this arrangement, when said jib lengths are in fully retracted position, the overall size is reduced which is convenient for transportation purposes and for the force which is necessary for the raising action.

As previously stated, the first jib length 27 is hinged at 28 to the mast top and is held horizontally during operation by the guys 29, the set of beams 30 and the rear tie bars 33, 34. As clearly visible in FIG. 4, the jib length 27 has an open rectangular crossesectional open at its lower end and its upper members are constituted by U-shaped channels 41 through which rollers 42 fixed to the second jib length can be moved.

The jib length 40 has (as shown) a triangular cross section and carries adjacent its foot end a series of rollers 42 which performs its guiding action through the first jib length. The lower member of the jib length 40 is constituted by an I- shaped member 43 along which the rollers 44 of the crane trolley 45 may roll.

As visible in FIG. 5, the lifting cable 46 of the crane which extends'from a winch (not shown) in conventional manner is trained over a jockey pulley 47 provided at the top end of the mast, then over the pulley 48 of the trolley 45, over another jockey pulley 49 situated at the top end of the jib, then over another jockey pulley 50 provided at the foot end of the second jib length 40 until finally said cable is fixed at 51 to the end of the first jib length 27. Owing to this arrangement, the longitudinal extent of the cable and consequently the position of the lifting book 32 heightwise remain unaltered irrespective of the telescoping position of the second jib length 40. As the telescoping motion takes place, the hook 52 is consequently displaced horizontally.

In FIG. 6 is shown the method for controlling the telescop ing action of the crane jib. There is provided to that effect a reciprocatory device comprising an endless cable 53 extending from a special winch 54 and trained over a pair of pulleys 55 arranged at the foot end of the crane jib and over a horizontal jockey pulley 56 provided at the end of the first jib length 27, one run of said cable being fixed as shown at 57 to the second jib length 40. It will be easily understood that control of the cable 53 permits a selective displacement of the second jib length 40.

Asalso visible in FIG. 6, an endless cable 58 is engaged around the second jib length 40 and trained over four pulleys 59. This cable 58 is secured at 60 to the crane trolley 45 and at I 61 to the end of the first jib length 27. It will be understood whereas it is-brought back to the foot end of the jib when its length 40 is inwardly moved or retracted. One control mechanism thus operates the telescoping action of the crane jib and the motion of its trolley therealong. Such a construction permits the longitudinal extent of the crane jib to be reduced for transportation purposes without requiring any hand manipulation while leaving all cables in operative position and without an additional mechanism.

As previously stated, the crane jib may be made up of more than two lengths if this is desired. The construction then remains the same but the last jib length then carries the crane trolley.

In FIGS. 7 and 8, 63 designates the first stationary length or section of a horizontal telescopic crane jib which generally speaking is of the same general type as described hereinbefore and is held at its end by the jib guy 62. Sixty-four designates the second (movable) jib length or section. The other parts of the crane which are identical with those that are visible in FIGS. 1 to 6 are not represented for the sake of legibility of the drawings.

It will'be seen from these two figures that the second jib length 64 has a cross-sectional area smaller than that of the first jib length 63. Said length 64 is guided by a first series of rollers 66 bearing on the lower face of the first jib length 63' adjacent its end, also on additional rollers 67 distributed throughout the length of said first jib length. The loading strain supported by the second jib length .64 is taken by a secondseries of rollers 68 provided at the foot end of the second jib length over its upper part, said rollers bearing upon the lower face of the upper part of the first jib length 63.

In the present case, the first jib length 63 is providedat its lower end with a pair of members forming a rolling track 64 for the rollers 70 of the trolley 71. The second jib length 64 carries adjacent its free end, which remains outside the first jib length 63 itself in the fully telescoped position shown in dotted lines in FIG. 1, two chassis elements which together form a rolling track 72. When the second jib length 64 occupies a fully retracted or telescoped position, the track 72 forms a continuation of the rolling track 69 pertaining to the first jib length 63.

Reference being had to FIG. 7, it will be seen that in an arrangement similar to the one reading on FIG. 5, the lifting cable 73 extending from the winch (not shown) is trained over a pulley 74 arranged at the head end of the mast, then over the pulleys of the trolley 71, over a jockey pulley 75 fitted at the free end of the second jib length 64 and over another jockey pulley 76 situated at the foot end of said second jib length, and is fastened at a point 77 adjacent the head end of the first jib length 63. This arrangement ensures, as telescoping action of the crane jib occurs, such a compensation of length that the lifting hook 78 may perform a horizontal motion.

In FIG. 8 is shown the arrangement adopted for the cable 79 that is used for controlling the trolley and for performing the telescoping action as shown at 71. The cable 79 which extends from the directing winch (not shown) is first trained over a pulley 80 provided at the head end of the mast and is secured .to the trolley 71 at 81. Another cable run 82 extending from the securing point 81 is trained over a jockey pulley 86 provided at the free end of the second jib length 64 and then back inside the latter to a second jockey pulley 83 provided at its foot end, then over a horizontal jockey pulley 84 provided on the first jib'length 63 and finally over a jockey pulley 83 provided at the foot end of said first jib length before reaching the directing winch. Owing to this arrangement, adequate control of the trolley motion over the first jib length is accomplished, also the telescoping action of the second jib length carrying the trolley at its end.

Reference will now be made to FIGS. 9 to 11 which show the double-locking device permitting Control of the trolley and telescoping action from one and the same winch.

The second jib length 64 carries adjacent its end portion a hook 87 pivotally supported at 88 by said length and connected by a rod 89 with a lever 90 urged by a traction spring 91. In operative position, the beak of the hook 87 cooperates with a dog 92 provided on the first jib length 63 so as to interlock the two jib lengths in the fully telescoped position in which the two rolling tracks 69, 72 form mutual extensions of each other. In this condition, the trolley 71 may pass over from one jiblength to the other.

Such a device permits any separation of the two rolling tracks 69, 72 to be avoided as long as the trolley 71 is not on the second jib length 64. In order to ensure an unlocking action after the trolley has passed over the second jib length, said trolley carries an abutment 93 which engages the lever 90 (as shown in FIG. so to move the hook 67 off the dog 92 as the trolley reaches the end of the second jib length. The latter may be then disengaged from the first jib length.

in order to hold the trolley 71 on the second jib length 64 as long as the latter has not been brought back to a fully telescoped condition i.e. aslong as the rolling tracks 69, 72 are not inabutted relation, there is provided on the second jib length a hook 95 pivotally supported at 96 and associated with a rod 97 cooperating with a compression spring 98 which normally holds the hook 95 in operative position, said rod terminating in an abutment 99. Another abutment 100 is provided on the first jib length. The trolley carries a hooking dog 101.

ln the position shown in FIG. 1 1, it will be seen that the trolley is held on the second jib length 64 and is operatively connected therewith. When both jib lengths reach the fully telescoped position (as visible in FIG. 10) the abutments 99, 100 cooperate so as to control raising of the hook 95 which then frees the dog 101. The trolley can then freely move on the first jib length.

The entire movement takes place as follows: Assuming the trolley to be at the foot end of the jib, control of the directing winch forwardly acts through the cable run (FIG. 8) to'cause the trolley to be moved forward to the end of the first jib length 63, whereafter the trolley passes over the second (movable) jib length 64. When reaching its end, its abutment 93 hits the lever 90, thereby operating the hook 67 for freeing the jib length 64 which is then moved forwardly by the cable run situated between the two jib lengths as far as a fully extracted position is reached. During this movement, the lifting hook 78 of the crane effects a horizontal motion. Reverse movement takes place in a similar fashion, namely reverse control of the directing winch performs, through the cable 79 (FIG. 8) rearward movement of the second jib length by the action of the hook 94. When this second jib length reaches the fully telescoped position, the abutments 100, 99 cooperate for operating the hook 95 and liberating the trolley 71 which then passes over the first jib length 63. During this movement, liberation of the lever 90 takes place, whereupon the two jib lengths 63, 64 are interlocked. The'trolley then continues its motion until the foot end of the jib is reached. Here again the movement of the lifting hook 78 is horizontal.

Minor constructional details may be varied without departing from the invention within the ambit of technical equivalencies.

, lclaim:

1. A .tower crane comprisinga horizontal jib, a carrier frame, a revoluble orientatable superstructure, a slewing.

device for mounting said superstructure upon said frame, a mast supporting said jib and including a first lower element hinged at one end to the superstructure and a second upper element hinged at one end to the other end of said first element, a carriage guided on said first element, a mechanism for controlling motion of said carriage upon said first mast element, a rod connected with said carriage and a stationary pivotal point on the superstructure at a distance from the hinge of the first mast element to the superstructure, and a mechanism causes owing to the carriage motion a movement of the first mast element with respect to the superstructure and a movement of the second mast element relative to the first element. I

2. A tower crane according to claim 1 having a pedestal on the superstructure, the rod being connected with the carriage and pedestal at a distance from the pivotal point of the lower mast element upon the superstructure.

3. A tower crane according to claim 1 wherein the carriage includes a nut portion and the carriage control mechanism comprises a lead screw and a power reducer unit for revolving said lead screw.

4. A tower crane according to claim 1 comprising a pedestal on the superstructure, a hinge on said pedestal at a distance from the pivotal point of the first lower mast element on said superstructure, a rod connected with said pedestal hinge and with the carriage so as to hold the first mast element inoperative in a horizontal transporting position horizontally aligned with said superstructure, and a second upper mast element whose length is larger than that of said first element and havingan inoperative position overlying said first element and said superstructure.

5. A tower crane as claimed in claim 1 said first jib comprising a first jib length hinged to the end of the second mast element remote from said first element, a second jib length of telescopic structure with respect to said first jib length, and means for controlling telescopic motion of the second jib length with respect to the first jib length.

6. Atower crane according to claim 5 wherein the first jib length has guiding rails and the second jib length is telescopically movable inside said first length and has means movable on said guiding rails. i

7. A tower crane according to claim 5 comprising jockey pulleys provided adjacent both ends of the second jib length and a lifting cable successively trained over said pulleys and secured to the end of the first jib length remote from the mast so as to provide a constant cable length and consequently a constant charge height for all telescoped positions of the jib.

8. A tower crane according to claim 5 wherein the means for controlling telescopic motion of the second jib length include jockey pulleys carried by the first jib length and a reciprocatory contrivance having a cable trained over said pulleys, one point of said cable being connected with said second jib length.

9. A tower crane according to claim 5 including guiding means on the second jib length, a lifting trolley movable on .said guiding means, jockey pulleys on said second jib length so as to define a closed path, and an endless cable trained over said jockey pulleys, one point of said cable being connected with the first jib length so that telescoping motion of the second jib length causes a motion of said trolley upon said second jib length.

10. A tower crane according to claim 5 comprising a first jib length having a cross-sectional area larger than that of the part of the second jib length which is engaged through said first jib length, a first set of rollers situated at the lower portion of the first jib length adjacent its free end, said second jib length resting upon said rollers, and a second set of rollers arranged at the upper portion of the second jib length, adjacent its endengaged through the first jib length and supported inside the upper portion of said first jib length.

11. A tower crane according to claim 5 comprising a first jib length having a cross-sectional area larger than that of the second jib length, which is engaged through said first jib length, a first set of rollers situated at the lower portion of said first jib length adjacent its free end, said second jib length resting upon said rollers, a second set of rollers arranged at the upper portion of the second jib length, adjacent its end engaged through said first jib length and supported inside the upper portion of said first jib length, and additional rollers distributed over the extent of the first jib length, adjacent its lower portion, so as to behave as a support for the second jib length. I a

12. A tower crane according to claim comprising a movable trolley on the second jib length, a control cable for said trolley, a pulley mounted at the foot end of the crane jib, said cable being trained over said pulley and being secured to the trolley, a pair of jockey pulleys arranged adjacent the ends of the second jib length, a further pair of jockey pulleys arranged adjacent the ends of the first jib length, and a cable fixed to the trolley and successively trained over said jockey pulleys of the first and second jib lengths. v

13. A tower crane having a horizontaljib comprising a carrier frame, an orientatable revoluble superstructure", a slewing device for mounting said superstructure upon said frame, a mast including a first lower element hinged at one end to said superstructure and a second upper element hinged at one end to an end of said first element, a carriage guided over said first lower element, a mechanism for controlling the movement of saidcarriage upon said first mast element, a rod connected with said carriage and with a stationary pivotal point on the superstructure at some distance from the pivotal point of said first mast element on said superstructure, a toggle system interconnecting the carriage, the first mast element and the second mast element, a first jib length hinged to the end of the second mast element remote from the end hinged to the first mast element, a second jib length engaged telescopically in said first jib length, means for controlling the telescopic motion of said second jib length through said first jib length, members providing a rolling track in the lower portion of the first jib length, further members providing a rolling track adjacent the end of the second jib length remote from the mast, adjacent the lower portion of said second jib length, in such positions that in full telescoped condition of the crane jib, the members of the second jib length form an extension of the members of the first jib length, and a lifting trolley capable of rolling upon said members of the jib lengths.

14. A tower crane according to claim 13 comprising a locking device for holding the second jib length in fully retracted position in the first jib length so long as the trolley is on said first jib length, and means for unlatching said locking device when the trolley arrives upon said second jib length.

15. A tower crane according to claim 13 comprising a first locking device for holding the second jib length in fully retracted position in the first jib length when the trolley is sup ported by the first jib length, means for unlatching said locking device when the trolley reaches said second jib length, a second locking device for holding the trolley on the second jib length as long as it is partly disengaged from the first jib length, and means for controlling the unlatching of said second locking device when the second jib length reaches a fully telescoped position with respect to the first jib length.

l 6. A tower crane according to claim 1 comprising a jib articulated at the upper end of the second mast element, a rear tie member including a first and a second parts hinged together, connecting the jib with the superstructure, and a connecting member joining the pivotal point between said two parts of the rear tie member at the pivotal point of the two mast elements. 

1. A tower crane comprising a horizontal jib, a carrier frame, a revoluble orientatable superstructure, a slewing device for mounting said superstructure upon said frame, a mast supporting said jib and including a first lower element hinged at one end to the superstructure and a second upper element hinged at one end to the other end of said first element, a carriage guided on said first element, a mechanism for controlling motion of said carriage upon said first mast element, a rod connected with said carriage and a stationary pivotal point on the superstructure at a distance from the hinge of the first mast element to the superstructure, and a toggle system interconnecting said carriage, the first mast element and the second mast element so that actuation of said mechanism causes owing to the carriage motion a movement of the first mast element with respect to the superstructure and a movement of the second mast element relative to the first element.
 2. A tower crane according to claim 1 having a pedestal on the superstructure, the rod being connected with the carriage and pedestal at a distance from the pivotal point of the lower mast element upon the superstructure.
 3. A tower crane according to claim 1 wherein the carriage includes a nut portion and the carriage control mechanism comprises a lead screw and a power reducer unit for revolving said lead screw.
 4. A tower crane according to claim 1 comprising a pedestal on the superstructure, a hinge on said pedestal at a distance from the pivotal point of the first lower mast element on said superstructure, a rod connected with said pedestal hinge and with the carriage so as to hold the first mast element inoperative in a horizontal transporting position horizontally aligned with said superstructure, and a second upper mast element whose length is larger than that of said first element and having an inoperative position overlying said first element and said superstructure.
 5. A tower crane as claimed in claim 1 said first jib comprising a first jib length hinged to the end of the second mast element remote from said first element, a second jib length of telescopic structure with respect to said first jib length, and means for controlling telescopic motion of the second jib length with respect to the first jib length.
 6. A tower crane according to claim 5 wherein the first jib length has guiding rails and the second jib length is telescopically movable inside said first length and has means movable on said guiding rails.
 7. A tower crane according to claim 5 comprising jockey pulleys provided adjacent both ends of the second jib length and a lifting cable successively trained over said pulleys and secured to the end of the first jib length remote from the mast so as to provide a constant cable length and consequently a constant charge height for all telescoped positions of the jib.
 8. A tower crane according to claim 5 wherein the means for controlling telescopic motion of the second jib length include jockey pulleys carried by the first jib length and a reciprocatory contrivance having a cable trained over said pulleys, one point of said cable being connected with said second jib length.
 9. A tower crane according to claim 5 including guiding means on the second jib length, a lifting trolley movable on said guiding means, jockey pulleys on said second jib length so as to define a closed path, and an endless cable trained over said jockey pulleys, one point of said cable being connected with the first jib length so that telescoping motion of the second jib length causes a motion of said trolley upon said second jib length.
 10. A tower crane according to claim 5 comprising a first jib length having a cross-sectional area larger than that of the part of the second jib length which is engaged through said first jib length, a first set of rollers situated at the lower portion of the first jib length adjacent its free end, said second jib length resting upon said rollers, and a second set of rollers arranged at the upper portion of the second jib length, adjacent its end engaged through the first jib length and supported inside the upper portion of said first jib length.
 11. A tower crane according to claim 5 comprising a first jib length having a cross-sectional area larger than that of the second jib length, which is engaged through said first jib length, a first set of rollers situated at the lower portion of said first jib length adjacent its free end, said second jib length resting upon said rollers, a second set of rollers arranged at the upper portion of the second jib length, adjacent its end engaged through said first jib length and supported inside the upper portion of said first jib length, and additional rollers distributed over the extent of the first jib length, adjacent its lower portion, so as to behave as a support for the second jib length.
 12. A tower crane according to claim 5 comprising a movable trolley on the second jib length, a control cable for said trolley, a pulley mounted at the foot end of the crane jib, said cable being trained over said pulley and being secured to the trolley, a pair of jockey pulleys arranged adjacent the ends of the second jib length, a further pair of jockey pulleys arranged adjacent the ends of the first jib length, and a cable fixed to the trolley and successively trained over said jockey pulleys of the first and second jib lengths.
 13. A tower crane having a horizontal jib comprising a carrier frame, an orientatable revoluble superstructure, a slewing device for mounting said superstructure upon said frame, a mast including a first lower element hinged at one end to said superstructure and a second upper element hinged at one end to an end of said first element, a carriage guided over said first lower element, a mechanism for controlling the movement of said carriage upon said first mast element, a rod connected with said carriage and with a stationary pivotal point on the superstructure at some distance from the pivotal point of said first mast element on said superstructure, a toggle system interconnecting The carriage, the first mast element and the second mast element, a first jib length hinged to the end of the second mast element remote from the end hinged to the first mast element, a second jib length engaged telescopically in said first jib length, means for controlling the telescopic motion of said second jib length through said first jib length, members providing a rolling track in the lower portion of the first jib length, further members providing a rolling track adjacent the end of the second jib length remote from the mast, adjacent the lower portion of said second jib length, in such positions that in full telescoped condition of the crane jib, the members of the second jib length form an extension of the members of the first jib length, and a lifting trolley capable of rolling upon said members of the jib lengths.
 14. A tower crane according to claim 13 comprising a locking device for holding the second jib length in fully retracted position in the first jib length so long as the trolley is on said first jib length, and means for unlatching said locking device when the trolley arrives upon said second jib length.
 15. A tower crane according to claim 13 comprising a first locking device for holding the second jib length in fully retracted position in the first jib length when the trolley is supported by the first jib length, means for unlatching said locking device when the trolley reaches said second jib length, a second locking device for holding the trolley on the second jib length as long as it is partly disengaged from the first jib length, and means for controlling the unlatching of said second locking device when the second jib length reaches a fully telescoped position with respect to the first jib length.
 16. A tower crane according to claim 1 comprising a jib articulated at the upper end of the second mast element, a rear tie member including a first and a second parts hinged together, connecting the jib with the superstructure, and a connecting member joining the pivotal point between said two parts of the rear tie member at the pivotal point of the two mast elements. 